Technical Field
This Patent Disclosure relates generally to resonant inductive sensors and sensing, such as can be used in sensing position or proximity.
Related Art
Inductive sensors include an inductive sensor (coil) that inductively couples to a conductive target within its sensing range. For example, inductive sensors are used to sense proximity/position of the target.
Resonant inductive proximity/position sensors use a sensor resonator (LC tank circuit) configured for operation in a resonance state (resonant frequency and amplitude). Sensor electronics drives an AC excitation synchronized with resonator oscillation voltage to maintain resonance (steady state oscillation), overcoming a resonator loss factor represented by a resonator impedance (such as a series/parallel resistance Rs/Rp). For example, in the case of inductive sensing, the resonator includes an inductive sensing coil that, operated at resonance, projects a magnetic sensing field.
Resonant sensing is based on changes in resonance state manifested by, for example, changes in resonator amplitude and frequency resulting from changes in resonator impedance in response to a conductive target. For example, in case of inductive sensing, resonance is affected by a storage or loss in projected magnetic flux energy output from the inductive sensing coil, such as caused by the eddy current effect associated with a conductive target. This sensor response is manifested as a change in resonator impedance (loss factor Rs/Rp).
Resonant inductive sensors operated with a conductive target (such as ferrous metallic) have a limited sensing range of about +/−50% of the sensor coil diameter. Using a target resonator configured for operation with the sensor resonator can extend this range to about 500% the sensor coil diameter. In this configuration, the sensor resonator and target resonator form coupled resonators.